I’ll also note, again IIRC, it’s the box art for the previous toys that showed us what their cutie marks would be, since they never had them in the movie (for obvious reasons.)
The last time they showed them as ponies, they were Earth ponies.
I think the unicorn this time was the idea that they used magic in the movie, so that would translate into unicorn as a pony. Personally I like the Earth pony design for them better.
It’s probably to help them sell. Some marketer probably concluded including Pony imagery might help link them to FiM.
Honestly I wouldn’t mind official Spike-pony.
They are sirenes, not ponies.
Not every sentient creature is a pony.
What’s next; official Spike-pony?
Flutterpony.
https://derpibooru.org/617097?scope=scpe320972012984e9ac64cef076b6b27be4d38a8b61
Although not Cannon, Sonata Appears as a Earth pony with no wings in the Trading Card Game.
https://derpibooru.org/1017488?scope=scpece0f64510f6b14ed6a20ac9a60d7a1e85be15f2d
Edited
So they’re not fan made, they’re official.
On the box-iverse anyways.
Well, I think they were shown with their gems in pony form. It was on the packaging for their EQG:RR dolls, IIRC.
Earth pony post gem, Unicorn pony with gem?
I think the unicorn this time was the idea that they used magic in the movie, so that would translate into unicorn as a pony. Personally I like the Earth pony design for them better.